1. Field of the Invention
The present invention relates to a circuit for detecting motion of pictures in HDTV (High Definition Television) receiver, and in more particular to a motion detection circuit for use in the HDTV receiver for receiving a bandwidth compressed television transmission signal.
2. Description of the Prior Art
A multiple subsampling transmission system that achieves interframes and interfields offset subsampling, is one of various methods to transmit a television signal, that is, HDTV picture signal by bandwidth compression. An embodiment of such a transmission system is called MUSE (Multiple Sub-Nyquist Sampling Encoding) system, which performs effective bandwidth compression in transmission of television picture signals.
The multiple subsampling transmission system conventionally includes means for processing a still picture-area (portions of a field where the picture is still), means for processing a moving picture-area, a motion detector for detecting motion information from a difference signal of adjacent interframes, a mixer for mixing the moving picture with the still picture in accordance with a motion amount detected from the motion detector, and means for interframe offset sampling a signal from the mixer.
Further, the means for processing the still picture-area generally includes an interfield prefilter for removing high-frequency components in an oblique direction of a picture signal with a 24 MHz bandwidth limitation, a sampling circuit for receiving a signal from the interfield prefilter and for performing interfield offset subsampling in the 24 MHz sampling frequency, and a sampling frequency converter for changing only the sampling frequency from 24 MHz to 32 MHz.
Furthermore, the means for processing the moving picture-area generally includes an intrafield prefilter for limiting in 12 MHz a frequency bandwidth of the picture signal with the above-described bandwidth limitation and for removing the high-frequency components in the oblique direction, so as to prevent occurrence of aliasing, a sampling circuit for sampling an output of the intrafield prefilter in the 24 MHz sampling frequency, and a sampling frequency converter for changing only the sampling frequency from 24 MHz to 32 MHz.
The moving and still pictures, are each output by their respective processing means, are mixed together in linear mode by the mixer, according to an amount of motion detected by the motion detector. To an output of the mixer, the interframe offset subsampling is taken at 16 MHz sampling frequency by the interframe offset subsampling means, so that the moving picture signal would not have any aliasing portions in the 0 to 4 MHz frequency band. Along with various control signals necessary to reconstruct the original picture in a receiving end, for motion vector to compensate a movement of picture that may result from movement or tilting of a camera, the subsampling signal is transmitted in a 8 MHz base band for example.
FIG. 1 is a block diagram illustrating a portion of a decoder in a receiving end of the above-described system. A picture signal separated from a multiple subsampling transmission signal delivered from a transmitting end, is applied to an input terminal 10. An interframe interpolation filter 13, a sampling frequency converter 14 and an interfield interpolation filter 15 constitute a still picture processor 12 for reproducing a still picture portion out of the picture signal received. Here, by replacing a picture element not sampled by the interframe offset subsampling with a picture element of a preceding frame, the interframe interpolation filter 13 processes the still picture. The sampling frequency converter 14 converts a frequency of the interpolated output of the interframe interpolation filter 13 to the 24 MHz sampling frequency from the former 32 MHz frequency. In order to obtain a still picture with a 24-MHz signal band without aliasing, the interfield interpolation filter 15 is adopted. In addition, the interframe interpolation filter 13 and the interfield interpolation filter 15 serve to compensate for a motion of the picture resulting from a panning phenomena such as movement or tilting of the camera, in response to a motion vector provided from a separator (not shown in the drawing).
An intrafield interpolation filter 17 and a sampling frequency converter 18 constitute a moving picture processor 16 for reproducing a moving picture portion out of the picture signal received. The intrafield interpolation filter 17 is used to reproduce a moving picture signal without aliasing in a 0 to 12 MHz frequency band, from a moving picture signal aliased in 4 to 8 MHz frequency band. The sampling frequency converter 18 changes a frequency of the reproduced moving picture signal to the 24-MHz sampling frequency from 32-MHz signal.
A motion detector 20 limits a bandwidth of and the input signal up to 4 MHz to obtain an adjacent interframe difference signal, that is, an amount of motion from the moving picture signal. The still picture of the still picture processing means 12 and the moving picture of the moving picture processing means 16 are mixed together in a linear mode at a mixer 22, according to the amount of motion delivered from the motion detector 20, and thereafter applied to a Time Compressed Integration (TCI) decoder, not shown in the drawing.
U.S. Pat. No. 4,692,801, which was issued on 8 Sep. 1987, discloses the aforesaid system (MUSE II).
A method of detection of a motion area in the receiver of the aforesaid system is, to obtain an adjacent interframe difference signal from a moving picture signal of the picture signal received and then carry out the linear mixing operation of the still picture and the moving picture according to an amount of motion of said interframe difference signal.
In the meanwhile, referring to another MUSE system (see U.S. Pat. No. 4,745,459) including a frame memory and a temporal interpolator as a so-called still picture processing means, further having a spatial interpolator as a so-called moving picture processor, the motion detector achieves detection of such a motion area owing to a difference signal of two adjacent interframes.
Hence, the above-described prior art system generally has a problem owing to complication of detection of the motion area. Moreover, the complication of its circuit construction in the receiver will make it difficult to achieve economy its cost.